Casts of the type used to set broken bones, for example, are made of plaster, as well as various synthetic resin materials, such as the fiberglass/resin composite sold under the trademark "SCOTCHCAST" by the Minnesota Mining and Manufacturing Company of St. Paul, Minn. U.S.A., and/or described, for example, in U.S. Pat. Nos. 4,502,479; 4,609,578; 4,667,661; 4,705,840 and 4,774,937. Advantages of fiberglass/resin composite materials include gas permeability, light weight, and transparency to X-rays.
Casts ordinarily consist of a tubular stockinet or an elongate strip or bandage that is placed or wrapped, for example, around a patients injured limb, a layer of synthetic cast padding wrapped around the stockinet, and a plurality of layers of the fiberglass-resin composite or plaster material wrapped around the padding to form a rigid shell. Such cast padding and stockinet is typically made from very flexible woven or nonwoven materials, such as cotton, polyester or other fibers. Cast padding and stockinet will sometimes be collectively referred to herein as "wrapping".
Cast shells have typically been removed by using powered oscillating saws, which are noisy and may create a substantial quantity of dust. In order to prevent injury to the patient, these saws are usually adapted to be oscillated at a high frequency and low amplitude. Despite that precaution, the saw can cause burns or cuts in some situations, and notwithstanding any actual danger, patients, especially small children, may be frightened by the saw. U.S. Pat. No. 4,637,391 (Schlein) describes a surgical saw blade for cutting plaster or fiberglass casts. That saw blade is adapted to oscillate at high frequency (e.g., 12,000-14,000 oscillations per minute) and low amplitude. An adjustable depth stop is provided to limit the depth that the saw blade may cut.
U.S. Pat. No. 4,421,111 (Rothman) describes a surgical cast cutter that includes a saw blade that is oscillated at low amplitude to prevent injury of the patient. That cutter includes the feature of vacuum exhaust of dust particles created in cutting the cast. British Patent No. 2 068 829 (Saito) and U.S. Pat. No. 4,543,718 (Duescher) describe other cast cutters employing oscillatory motion and vacuum exhaust of dust particles.
In addition to the creation of dust, one problem with oscillating cast cutters is that typically they do not cut through the soft layers or wrapping of the cast. This is because the low amplitude, high frequency motion of the blade is usually ineffective against soft tissue or fabric. As a result, the soft layers or wrappings underlying the cast are typically removed as a separate step after cutting the cast. For example, U.S. Pat. No. 3,365,798 (Cunningham) describes a device for cutting the soft wrappings underlying plaster casts after the shell has been cut. That device includes a shoe which may be positioned between the wrappings and the patient and two inwardly-facing intersecting blades that cut the wrapping as the device is pushed or pulled through a slot cut in the cast.
Another method of protecting a patient from the saw blade of a cast cutter has been to place a guard between the patient and the saw blade. For example, U.S. Pat. Nos. 2,344,262 (Odierna et al.) and 2,366,017 (Fortune) describe powered cast cutters including a guard or shoe for protecting the patient from the saw blade, with the guard or shoe separating the saw blade from the patient's skin. The shoe of those cutters are placed under the cast (i.e., between the cast and the patient's skin).
U.S. Pat. No. 590,163 (Pearson) describes a manually operated cast cutting tool having a guard for protecting the patient from the saw blade. That guard includes a foot that is positioned between the cast and the flesh of the patient. A crank-arm is provided for manually rotating the saw blade. U.S. Pat. No. 2,571,527 l(Boyer) shows another cast cutter having a guard that is placed between the cast and the patient. U.S. Pat. No. 2,217,923 (Silverman) shows powered and manually operated cast saws that include a guide shoe having a semi-circular groove for receiving the saw blade to accommodate different thicknesses of casts.
U.S. Pat. No. 1,269,373 (Brinck) describes a cutting device having a shield plate that is slipped between the cast and the patient, and a circular cutting member that is movable relative to the shield plate as the cast is cut. That device includes a crank for rotating the cutting member, and a pin to limit motion of the cutting member toward the shield plate as the cast is cut.
U.S. Pat. No. 2,232,733 (Scarboro) shows a powered cast remover that includes a guard that separates the saw blade from the patient and a suction fan for removing the cuttings and placing them in a container.
While cast cutting devices that employ a guard between the cast and the patient and a conventional rotary saw blade may efficiently, quietly and safely cut the rigid shell of the cast, it has been found that they are ineffective at cutting the flexible wrappings underlying the shell. The wrappings are frequently caught by the teeth of the saw blade and wrapped around the axle of the saw blade, with the result that such devices have typically become jammed on the cast shortly after starting the cut (e.g., within 4-6 inches (100-150 mm)).
U.S. Pat. No. 4,611,585 (Steidle) describes a cast cutter that includes a fixed center blade that is positioned between the cast and patient and two motor-driven oscillating blades disposed along opposite sides of the center blade. That cutter includes a movable cover hood which apparently ensures that the blades are only exposed when the blades are applied to the plaster cast itself.
Casts have also been cut by embedding wire in the cast material when forming the cast, and pulling the wire to cut the cast. For example, U.S. Pat. No. 4,290,424 (Wahl et al.) and British Patent No. 2 003 391 (Lampke et al.) show cutting wires that are embedded in the material of the cast. See, also, West German Patent No. 3 342 918 (Strang).